In carrying out domestic and/or industrial washing and bleaching, use is generally made of commercial detergents in which a bleaching agent is incorporated, together with various fundamental constituents and additives normally contained in such detergents. The incorporation of a bleaching agent in commercial detergents at their production stage gives rise however to a certain number of problems, both with regard to the initial choice of the bleaching agent to be incorporated, and with regard to the further behavior of the detergent incorporating the bleaching agent (during storage and/or washing and/or after discharging the used water).
Those detergents containing a bleaching agent which are mostly available commercially at the present time are solid detergents (essentially in powder form), in which the bleaching agent most often consists of sodium perborate tetrahydrate. It is generally admitted that sodium perborate constitutes a very effective bleaching agent, provided the wash bath is raised to a temperature close to boiling point. The bleaching action of the perborate is relatively weak at lower wash temperatures (below 60.degree. to 78.degree. C.), and this constitutes a particularly important drawback in the present energy saving context. Attempts are made at the present time to add activators to these solid detergents for decomposing the perborate in order to allow washing and bleaching at lower temperatures. However these attempts have not at the moment proved entirely satisfactory, and formulations containing such activators are relatively costly. The use of perborate as a bleaching agent in detergents gives rise to a certain number of other drawbacks, most of which are related to its often excessive concentration (generally exceeding 15 to 20% by weight). A too high perborate concentration can in fact lead to deterioration of the textile fibers (in particular cellulose fibres), and to a weakening of the shades of certain colors (certain dyes being in this respect highly sensitive to an excess of oxidant). An excessive perborate concentration, in the case of detergents containing enzymes, can also exert a prejudicial influence on the biological action of these enzymes, although the perborate and enzymes normally exert complementary actions in certain processes of stain destruction (pigmentary and protein stains). It is also well established that boron compounds contained in residual wash water exert harmful effects on the environment. In this respect, boron is to a certain extent toxic, and this is more marked in the case of higher plants than in the case of microorganisms and animals (antifertilising effect). As boron compounds cannot be eliminated by the conventional treatment processes for water, the result is that the content of boron derivatives in certain rivers reaches an abnormally high level, tending to make them unsuitable for irrigation. These problems of water pollution by boron compounds are becoming so preoccupying that they have led certain countries to make laws aiming to limit the concentration of perborate in detergents, or indeed to prohibit them completely. Finally, sodium perborate has certain technical drawbacks such as segregation into powder (high apparent density of the perporate grain), friability of the grain (interference of perborate dust with production technology and its effect on working hygiene), and low solubility in cold water.
In an attempt to overcome the aforesaid drawbacks, it has been proposed to replace the perborate by other bleaching agents, such as sodium percarbonate. The effectiveness of these replacement agents has however proved to be much lower from the bleaching aspect. The choice of bleaching agent to be incorporated in solid detergents is also obviously limited to solid compounds, and this excludes any possibility of adding a liquid bleaching agent such as hydrogen peroxide, which is well known for its bleaching properties.
Excellent liquid detergents have appeared on the market at the present time, these being normally sold without any bleaching action. The incorporation in these liquids of a liquid bleaching agent such as hydrogen peroxide thus becomes theoretically possible, and many proposals have been made in this sense. However, such incorporation at the production stage gives rise to serious practical problems. In this respect, it is well known that hydrogen peroxide is a relatively unstable compound (the more unstable the more dilute it is used), so that its incorporation into a liquid detergent requires the use of complexing or stabilising substances to ensure correct stability during prolonged storage (and to thus prevent a too high active oxygen loss with time). However the presence of such complexing substances means that the liquid detergent is much too stable when it has to be used, so that it is not able to liberate at that moment sufficient active oxygen, with a sufficiently rapid speed in order to give truly effective bleaching. Furthermore, an increase in the stability of hydrogen peroxide preferably requires an acid environment, and this is in relative contradiction with the general formulations of detergents, in which it is desirable to have basic constituents in order to facilitate washing and bleaching. In the case of detergents containing enzymes, incorporating hydrogen peroxide into such liquid detergents during their production can have the further negative consequence of disturbing the biological activity of such enzymes, both during storage and at the start of washing and bleaching.
It has been known for some time to prepare hydrogen peroxide electrolytically by reducing oxygen at a cathode in an alkaline medium. To the knowledge of the applicant, it has never been proposed up to the present time to integrate such an electrolytic preparation process with textile washing and bleaching operations.